1. Field of Invention
The present invention relates generally to a method of preventing the growth of a broad range of microorganisms on food products. More specifically, the present invention relates to a method of using quaternary ammonium compounds (QACs) for preventing the growth of a broad spectrum of microorganisms on food products; such as, meat products, for example, poultry, beef, pork, lamb, venison, and other edible meat products; seafood, for example, fish and shellfish; fruit, vegetables, and any other food products that can be treated utilizing the aqueous treatment methods of the present invention without detrimentally affecting the appearance, texture, and quality of the food. More specifically, the present invention relates to a method of using QACs to inhibit the attachment of, to remove, and to prevent the growth of microorganisms on food products. Particularly, the use relates to the effect of QACs on microorganisms that can cause foodborne contamination. More particularly, these microorganisms include microorganisms from the genus Staphylococcus, Campylobacter, Arcobacter, Listeria, Aeromonas, Bacillus, Salmonella, non-toxin-producing Escherichia, and pathogenic toxin-producing Escherichia, such as 0157:H7. More particularly, the present invention relates to an improved treatment method of spraying QACs on the food products to prevent broad spectrum microbial growth on these products. The present invention also relates to a formulation of QACs that makes the treatment method more amenable for commercial use in a food processing plant.
2. Description of the Prior Art
Prevention of foodborne illnesses by microbial contamination is of major concern to the food processing industry, regulatory agencies, and consumers. A recent report from the Food Safety & Inspection Service (FSIS) of the United States Department of Agriculture (Federal Register, Feb. 3, 1995) estimates that over 2 million cases of foodborne illnesses are produced annually by microbial contamination in the United States, with an associated cost of over $1 billion. Foodborne microbial contamination occurs both prior to entry into the processing facility, and by cross-contamination in the processing environment. The FSIS has instituted new Hazard Analysis and Critical Control Point (HACCP) requirements to reduce the occurrence and number of foodborne pathogens. These regulations must be met by food processors. Although the means of achieving this microbial reduction is left to the discretion of the processor, FSIS expects that antimicrobial treatments will be an important component of HACCP plans. The treatment methods of the present invention, which employ aqueous formulation of QACs, are useful in meeting the HACCP requirements.
In their efforts to provide a product completely free of microbial contamination, poultry and meat processors have encountered major difficulties in removing microorganisms that adhere or attach vigorously to poultry and meat tissues intended as food products. If contaminating microorganisms do not attach to the surface of the food, they can be easily rinsed off. However, the microorganisms that become strongly attached cannot be removed by rinsing and are quite resistant to removal by chemical or physical means.
Several chemical and physical methods have been proposed to reduce microorganisms in meat products, such as the use of chlorine or chlorine dioxide, ozone, hydrogen peroxide, lactic acid, sodium carbonate, trisodium phosphate, and electrical stimulation. Generally, these methods have shown limited effectiveness in reducing microbial contamination and may affect the physical appearance of the meat products.
Salmonella typhimurium contamination has been of special concern to the poultry processing industry because the organism is often present on live birds. Poultry processors have had great difficulty in removing microorganisms, such as S. typhimurium, that attach or adhere to poultry tissues. A variety of chemical and physical approaches have been suggested for use during poultry processing to eliminate S. typhimurium contamination of carcasses and minimize cross-contamination among carcasses. Trisodium phosphate (TSP) has been utilized in poultry processing for suppressing S. typhimurium; however, studies report conflicting results on the efficacy of TSP against Salmonella. As a result of its water solubility, TSP can be washed off of the poultry and thus, cannot inhibit attachment of microorganisms.
U.S. Pat. No. 5,366,983, incorporated herein by reference, discloses a method for removing or preventing Salmonella contamination of meat products by treatment with an effective amount of an aqueous solution of a QAC. Specifically, quaternary ammonium cationic surfactants, such as alkylpyridinium, particularly cetylpyridinium chloride (CPC) and cetylpyridinium bromide (CPB) were effective in removing S. typhimurium from poultry. This patent, however, does not disclose that QACs have a broader antimicrobial spectrum against any other genuses of food contaminating microorganisms than Salmonella. Further, it does not suggest that this treatment method would be effective on food products other than meat.
Food substances differ chemically and physically by virtue of their protein content, porosity, lipophilicity, surface pH, water permeability, surface area, and surface net electrical charge. Porosity of food could be important in the sequestration of bacteria whereas a tough, impermeable integument on a food substance could reduce bacterial contamination of the food. All of these chemical and physical differences among food products make it difficult to predict whether one antimicrobial agent's success on meat products would suggest success on other food products, such as fruit, vegetables, and seafood.
For example, CPC is known to bind to proteins; however, if the antimicrobial efficacy of CPC on food products were due in large part to the protein binding then the present method for treating non-proteinaceous fruits and vegetables would not have been expected to be successful.
Increasingly, foodborne illnesses caused by other pathogenic and spoilage bacteria than Salmonella have become a problem for food processors. A list of these bacteria with the products in which they have been identified is presented in Table 1:
TABLE 1 ______________________________________ INCIDENCE OF PATHOGENIC AND SPOILAGE BACTERIA Microorganism Poultry Beef Pork Pathogen Spoilage ______________________________________ Aeromonas hydraphila X X X X Arcobacter butzleri X X X Bacillus cereus X X X X Campylobacter jejuni X X X X Escherichia coli X X X X O157:H7 Listeria monocytogenes X X X X Salmonella typhimurium X X X X Staphylococcus aureus X X X X ______________________________________
Among these contaminating microorganisms listed in the table, Escherichia coli 0157:H7 is of special concern because of its virulence, severity of the illness produced, and associated mortality. E. coli 0157:H7 produces strong "shiga-like" toxins that lead to blood clotting abnormalities, kidney failure (hemolytic uremic syndrome), and death. Even if recovery from the acute illness is complete, 15-30% of infected people with hemolytic uremic syndrome will have evidence of chronic kidney disease. The risks associated with contamination with E. coli 0157:H7 are compounded by its reported resistance to antibiotics. In 1993, between 8,000-16,000 cases of foodborne illnesses were produced by E. coli 0157:H7 with an estimated cost of between 0.2 and 0.5 billion dollars.
Another virulent food contaminant, Listeria monocytogenes has been found in meat, vegetables, and various milk products; and may cause sepsis, meningitis, and disseminated abscesses. L. monocytogenes is a cold tolerant microorganism capable of growing under refrigeration. In 1993, about 1,700 cases of foodborne illness were produced by L. monocytogenes with an estimated cost of between 0.1 and 0.2 billion dollars.
Another microorganism of concern in the food industry is Aeromonas hydrophila which causes spoilage in the food and meat processing industry and reduces the shelf life of these products.
Presently, there are no known microbicidal compounds which are effective at preventing and removing contamination in a broad range of food products against a broad spectrum of gram positive, gram negative, aerobic, facultative anaerobic, and microaerophilic microorganisms. The present inventors have determined that QACs are effective against a broad spectrum of different microorganisms which produce foodborne illnesses when they become attached to a broad range of food products. This sensitivity of a broad spectrum of pathogenic microorganisms could not have been predicted.
Sensitivity of a microorganism to a particular antimicrobial agent is not predictive of the sensitivity of other microorganisms to the same agent. It is believed that antiseptics or germicides have a continuous spectrum of activity but the relative susceptibilities of different microorganisms must be considered. For example, the germicide, hexachlorophene is primarily effective against Gram positive microorganisms, and cationic antiseptics are not effective against sporulating organisms. Some Gram negative microorganisms, such as Pseudomonas cepacia, have been known to grow in solutions of the drug, benzalkonium chloride. Other bacteria have been known to be capable of growing in 70% ethanol (Harvey, S. C., Antimicrobial Drugs in Remington's Pharmaceutical Sciences, 18th Ed., Mack Publishing Co., pp. 1163-1241 1990).
In regard to the treatment of food products, it has been reported that Listeria is more resistant to the action of TSP than Salmonella or E. coli (Somers, E.B. et al., Int. J. Food Microbiol., 22:269-276, 1994). Further, (Breen et al., J. Food Sciences, 60:1991-1996, 1995) demonstrated that TSP is much less effective in inhibiting Salmonella growth than it is in detaching this organism. Similarly, TSP has reduced the numbers of E. coli 0157:H7 on chicken carcasses but is ineffective in inhibiting the cross-contamination of this microorganism to other chickens.
The present invention shows that QACs are effective against E. coli 0157:H7 in suspension in liquids, in reducing the numbers of this bacteria when it is attached to food products, as well as in inhibiting the attachment of this bacteria to food products. It has been reported that E. coli 0157:H7 shows resistance towards broad spectrum antimicrobial agents, such as tetracycline, streptomycin, sulfisoxazole (Kimet al., J. Infect. Dis., 170:1606-1609, 1994) and oxytetracycline (Ciosek et al., Med. Weter. 40:335,338:1984), whereas these same agents are very active against regular non-toxin-producing strains of E. coli.
Clearly the effectiveness of an antimicrobial agent or biocide against a particular microorganism cannot be predicted based upon its effectiveness against a different microorganism. There are many factors to consider, such as microbial characteristics which may play a role in the effectiveness of an antimicrobial agent against a particular microorganism. These characteristics include but are not limited to: (1) the degree of glycocalyx formation by a given species of attached microorganism, (2) the presence of a lipopolysaccharide- and phospholipid-containing cell envelope in gram negative bacteria, (3) the presence of lipoprotein as in most enteric bacteria and Pseudomonas, and (4) the presence of porin protein channels, for example in E. coli and Salmonella (Fulton et al., Structure in Medical Microbiology, 3rd Ed., pp. 37-54, 1991).
The food processing industry is in need of a more effective process for the prevention of growth of a broad range of contaminating microorganisms on many different food products. This is especially true for microorganisms which are attached to the surfaces of food. As a result of increasing numbers of illnesses caused by foodborne pathogenic microorganisms, the food processing industry now requires more effective processes for the removal and prevention of a broader spectrum of microorganisms, and particularly for pathogenic microorganisms, such as, toxinproducing Escherichia, i.e., E. coli 0157:H7, which are known to cause serious human diseases as a result of food contamination. The present inventors have provided a method of preventing the growth of microorganisms in liquids associated with food products, an important goal in preventing cross-contamination inside the processing plant; in removing attached microorganisms from food products, in inhibiting the attachment of microorganisms to the food products; and in preventing the growth of microorganisms that remain attached to the food products. Further, the method of the present invention can easily be adapted for use in a food processing plant.
Additionally, the present invention provides a concentrated QAC formulation for use in dilution to a working solution for use in the present method. A formulation of the present invention contains solubility enhancing components which may also result in longer contact times of the formulation with the food product.